The treatment of chemical waste is a topic of vital concern to industry and to all those concerned with the environment. Increasingly, governmental regulations are aimed at controlling the type and quantity of waste materials generated by industry because of the potential effect on the environment. As a result, treatment methods which reduce or eliminate chemical waste are of great interest to industry.
The automotive paint and coatings industry is a major source of chemical wastes. It is estimated that nearly 40% of the 6 gallons of paint used to produce the exterior finish on an automobile ends up as waste. With an estimated 36 million cars built each year (not including light trucks and other vehicles), the waste generated from painting alone approaches one quarter of a billion pounds. If this waste paint could be turned into a useful product, a major source of chemical waste could be reduced or eliminated.
When an automobile is painted on an assembly line, the excess paint is collected beneath the automobile in A trough filled with water. Typically, the waste paint solids are recovered by placing the paint-water mixture into large settling tanks. The paint solids either agglomerate as a raft on the surface of the water, or they sink and accumulate on the bottom of the tank. Other methods for treating the paint-water mixture to remove the paint solids are disclosed in U.S. Pat. Nos. 3,764,013 and 4,100,066. The material recovered from such processes is known as paint sludge.
Paint sludge is very complex material. The paint component contains uncured polymer resins, pigments, curing-agents, surfactants, and other minor formulation ingredients. In addition, paint sludge contains water and a variety of other solvents. The presence of the uncured paint resins, which cure and form a film upon heating, make the sludge very sticky and difficult to handle. Therefore, detackification agents are often added to the sludge.
The raw detackified paint sludge is usually disposed of without further processing. It is a tackfree, pulpy, putty-like solid having about 25% residual water. The cost and the environmental impact of disposing of paint sludge in this form make it undesirable.
Recently, a process was developed in which the detackified sludge is converted to a dry powder prior to disposal. The first step of this process, which is disclosed in U.S. Pat. No. 4,980,030, involves removing a portion of the water and liquid hydrocarbons from the sludge. The high solids sludge is then heated to remove the remaining water and hydrocarbons. The heating step is also designed to cure the uncured polymeric paint resins. The process is advantageous because it reduces the volume of waste produced, and the resulting powder is somewhat easier to handle than the wet sludge.
However, because the process disclosed in U.S. Pat. No. 4,980,030 involves curing the polymeric paint resins in the sludge, the dry particulate material formed is extremely hard, very abrasive, and difficult to reduce in size. The extreme hardness and large particle size of this powder preclude its use as, for example, a filler in sealants and adhesives without further processing.
Additional advantage could be achieved if a practical use could be found for the powder produced. One potential use for the powder is a filler in adhesives and sealants. Almost all sealants and adhesives contain an inert filler as a part of their composition, usually ranging from 10 to 50% by weight. Fillers are generally materials of fine particle size that are dispersable in organic media without the effects of settling. They are used to modify the properties of more costly ingredients. If paint sludge could be converted to a small pliable, tackfree particles, they could be used in adhesives and sealants as a filler. Although a dry powder is easy to handle and store, it is not necessary that the sludge be converted to a dry powder form. Any soft, pliable substance, such as a putty, could also be incorporated into the sealant.
Therefore, there remains a need for a process which will convert wet paint sludge into a form that is unsealable as a filler and can be easily incorporated into a sealant. One form could be a dry powder which is softer, less abrasive, and easier to reduce in particle size than powders containing fully cured polymeric resins. Another form could be a putty that also can be easily incorporated into the sealant.